The invention is directed to a molded article for the absorption of airborne sound, to be used principally in the engine compartment of motor vehicles and particularly as a sound absorber inside partial and complete motor encapsulations.
Molded articles of the above type are known. For instance, DE 40 11 705 C2 discloses a molded article for the absorption of airborne sound of which the side directed to the sound source comprises Helmholtz resonators. The Helmholtz resonators are arranged in such a manner that the adjacent Helmholtz resonators located in the effective range of the respective Helmholtz resonator of a lower frequency, have resonance frequencies different from each other. Said known molded article is provided as a plate absorber which, for forming the integral Helmholtz resonators, is shaped in a corresponding manner, with the openings of the Helmholtz resonators remaining free. For moisture and the like penetrating through the resonator openings, discharge openings are provided. In the context of the instant invention, a plate resonator is understood to be a soft, elastic, areal molded article which, when hit by airborne sound, is activated to undergo natural vibrations, the sound energy being transformed to heat.
The above molded articles have proven useful, but especially the covered frequency range as well as the degree of absorption suffer from inadequacy in many cases or for many cases, respectively. Further, although provisions have been made for drainage of liquids entering the resonators, residues and resultant impairment have been inevitable especially when using the molded article in the engine compartment.
It is an object of the invention to provide a molded article for the absorption of airborne sound which absorbs airborne sound in a consistent manner within a wider frequency range through a longer period of time.